I've only used the Pro version and at long last (after 18 months since initial release) I find it to be stable and reliable. I actually got my copy for free as I was part of the original beta test team and a free copy was reward for my efforts and input. Since then it has had more features added, more cameras and more platforms. Stability has always been variable until the most recent release - 1.9 for Windows - which I have found to be rock solid.
It is effective, but you still need to put the effort in to set up your target correctly and make sure the lighting is suitable. That would be true no matter which method you choose to use. However, once FoCal gets to work with its automated calibration you can sit back and relax rather than agonising over various images to decide which one is sharpest and without furious button twiddling to change settings in between shots.
There are many other ways to calibrate, but FoCal is the most automated that I know of. A close second is the DotTune method now making an appearance in the Magic Lantern software, but as far as I can tell that is crawling in its development beyond the 5D2 so don't hold your breath for that one.
Is it worth it? Well, if like me you have four bodies capable of AFMA and around 10 lenses (plus teleconverters on top of that) to mix and match with them then the answer is probably "Yes". On the other hand, if you only have one body and a couple of lenses it might be a bit of overkill - sledgehammer for walnut kind of thing.